Method of manufacturing synthetic diamonds

ABSTRACT

Synthetic diamonds are produced by subjecting carbonaceous material to heat and pressure in the presence of a metallic solvent having projecting portions.

United States Patent [151 3,652,220 Lindstrom [4 1 Mar. 28, 1972 [5METHOD OF MANUFACTURING 5s rm 0! Search ..23/209.1

SYNTHETIC DIAMONDS 56 References Cited [72] inventor: Cedric E.Lindstrom, Robertsfors, Sweden I 1 73 Assignee: Scandimant Aktiebollg,Robertsfors, UNITED STATES PATENTS Sweden 2,947,609 8/1960 Strong..23/209.1 22 Filed: M 13 1970 2,992,900 7/1961 Bovenkerk... ....23/2091 3,031,269 4/1962 Bovenkerk ...23/209.1 1 PP 37,425 3,124,422 3/1964Custers et al. ..23/209.i Rem Us. Application D." 3,407,445 10/1968Strong ..23/209. l X [63] Continuation of Ser. No. 612,483, Jan. 30,1967, Primary Examiner-Edward J. Meros abandoned. Attorney-Bailey,Stephens & Huettig [30] Foreign Application Priority Data [57] ABSTRACTFeb. 1 i, 1966 Sweden ..1754/66 Sy th ti diamonds are produced bysubjecting carbonaceous June 23, 1966 Sweden "861 material to heat andpressure the presence ofa metallic solvent having projecting portions.[52] US. Cl..... /209.1 [5 l 1 Int. Cl. 01b 31/06 3 Claims, 9 DrawingFigures METHOD OF MANUFACTURING SYNTHETIC DIAMONDS RELATED APPLICATIONSThis application is a continuation of application, Ser. No. 612,483,filed Jan. 30, 1967, now abandoned.

FIELD OF THE INVENTION The invention relates to the manufacture ofsynthetic diamonds.

THE PRIOR ART It is known that synthetic diamonds can be manufactured bysubjecting a mixture of particles of a non-diamond carbonaceous materialand particles of a solvent for carbon, for example iron or nickel or analloy containing one of these metals, to temperatures and pressures inthe diamond stable region, in which the temperature is sufficiently highfor the solvent to occur in molten form in the presence of thecarbonaceous material. It is also known instead of particles of solventto use bodies of the solvent which have a substantial extension inrelation to the reaction vessel, for example in the form of rods,cylinders, plates, etc.

SUMMARY or THE INVENTION According to the present invention it has beenfound possible to manufacture particularly large, well crystallizeddiamonds.

The present invention relates to a method of manufacturing syntheticdiamonds by subjecting a reaction mixture comprising a non-diamondcarbonaceous material and a solvent for carbon having the capacity toconvert the carbonaceous material to diamond in a reaction vessel, totemperatures and pressures in the diamond stable region, whereby thereaction mixture is heated by an electric current led through thereaction mixture to a temperature sufficiently high to melt the solventand the solvent is shaped as at least one body having a substantialextension in relation to the reaction vessel and arranged substantiallyperpendicular to the current direction, characterized in that thesolvent body is shaped with several narrowing or projecting parts, forexample in the form of peaks, points or ridges, facing the carbonaceousmaterial and that a negative temperature gradient is effected in thedirection from the carbonaceous material to the solvent body whenheating the reaction mixture.

The diamond stable region is the region above the equilibrium line forgraphite-diamond in the phase diagram for carbon published by Herman andSimon in Zeitschrift fiir Elektrochemie 59 (1955), page 333. ,m.

As is clear from the above, when carrying out the method according tothe invention the temperature is at least so high that the solvent ismelted in the presence of the carbonaceous material. Preferably atemperature of 50-250 C. above the eutectic melting point for a mixtureof carbon and the solvent should not be exceeded. Temperatures above2,200 C. should be avoided so that problems with the apparatus do notunnecessarily become more complicated.

The required minimum pressure is obtained in each case with a knowledgeof the temperature used, from said phase diagram for carbon. To avoidunnecessarily complicating the method it is normally suitable to use apressure not exceeding 120,000 atm.

Besides graphite, which is preferred, the carbonaceous material mayconsist of amorphous carbon, charcoal, anthracite or other naturallyoccurring carbon types, or of carbonaceous substances such as anthraceneand naphthalene which disintegrate under the prevailing reactionconditions to liberate carbon. The solvent may consist of iron, nickel,cobalt, platinum metals and other metals having the capacity to dissolvecarbon and convert carbonaceous material to diamond, or of alloyscontaining such metals, such as alloys consisting of nickel and iron, ofnickel, chromium and iron, of

nickel and chromium, of nickel, cobalt, chromium and iron, for examplestainless steel, and of nickel and copper. Compounds of said metals mayalso be used, such as carbides, for example iron carbide. All thesemetals, alloys and metal compounds having the capacity to dissolvecarbon and convert carbonaceous material to diamond are known per se andform no part of the present invention.

The carbonaceous material and solvent are subjected to pressures andtemperatures within the diamond stableregion for preferably 1 15 mins.However, it is also possible for them to be thus subjected for a longertime of the magnitude of l or several hours.

A possible explanation of the good result obtained according to theinvention may be that the narrowing or projecting parts of the solventbody in contact with the hotter carbon melt before the other parts ofthe solvent body, a rather limited number of diamond crystals then beingformed which then act as seeds for further crystal growth. This wouldthen take place during continued melting of the solvent body andcontinued dissolving of thecarbon.

The narrowing or projecting parts can be produced mechanically, forexample, by milling, stamping or drawing, the last mentioned if thesolvent body consists of a thread-like body, for example a spiral.Instead of several projecting parts, one long projecting part may beused, for example a continuous spiral ridge.

The solvent body may, inter alia, be in the form of a disc havingprojecting parts in the form of, for example concentric ridges or in theform of a continuous, for example spiral, ridge. It may also be in theform of a layer of balls arranged close to each other or as a flatspiral, which may be wound with its adjacent turns close to each other.

According to a particularly advantageous embodiment of the invention thesolvent body has several parts arranged with gaps between them which arefilled with the non-diamond carbonaceous material and this is alsoarranged around the solvent body as such. The parts of the solvent bodymay then form a continuous unit and the narrowing or projecting parts along narrowing or projecting part on the solvent body, facing thecarbonaceous material. the gaps between the parts.

According to a second embodiment of the invention having gaps betweenthe parts of the solvent body, these parts may have narrowing orprojecting parts facing the carbonaceous material arranged around thesolvent body as such and narrowing or projecting parts facing thecarbonaceous material arranged in the gaps between the parts.

When the solvent body is arranged with gaps between the parts it isparticularly advantageous to shape the solvent body as a loosely woundspiral, as several concentric rings or as a layer of balls arranged at adistance from each other.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be furtherexplained by describing a number of embodiments with reference to theaccompanying drawing which shows schematically a reaction vessel inwhich the carbonaceous material and the solvent body are heated andsubjected to the required pressure.

FIG. 1 shows the solvent body consists of a disc,

FIG. 2 shows a tightly wound spiral,

FIG. 3 shows a layer of balls arranged close to each other,

FIG. 4 shows a loosely wound spiral and FIG. 5 shows several concentricrings. FIG. 10, FIG. 2a, FIG. 4a and FIG. 5a show parts of the solventbody on a larger scale.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reaction chamber 10 shownin FIGS. 1 5 is cylindrical. It is limited sideways by an insulatingtube 1 1 of, for example talcum and at the top by two circular metalplates 12 and 13. The reaction chamber is heated electrically by leadingan electrical current through it in vertical direction. The pressure canbe generated, for example, with a vertically movable punch theinsulating tube 11 being surrounded by a pressureabsorbing casing and abearer being arranged at the end surface of the reaction chamber whichis not influenced by the movable punch.

Examples of-diamond manufacture according to the invention which can becarried out in the above exemplified reaction vessels are as follows:

EXAMPLE 1 In accordance with FIG. 1 the solvent body consists of a plate14 of a chromium-nickel alloy containing 20 percent by weight chromiumand 80 percent by weight nickel. The plate is arranged between twopre-compressed graphite cylinders 15 and 16. The plate is provided oneach side with projecting parts in the form of a continuous spiral ridge17 (FIG. la) with a height h of about l min. and a width b at the baseof about 1.5 mm., or in the form of several concentric ridges having,for example, the height and width mentioned. The projecting parts mayalso consist of several separate peaks arranged at a distance from eachother. The reaction mixture is heated by an electric current aspreviously mentioned to a temperature of about l,480 C. and subjected toa pressure of about 65,000 atm. for 2 minutes.

Due to the fact that the resistivity of graphite is considerably higherthan that of the metallic material in the solvent body, the graphitewill be heated to a higher temperature than the metallic solvent body bythe electric current passing between the metal plates 12 and 13. Anegative temperature gradient is thus achieved in the direction from thecarbonaceous material to the solvent body. Also in the followingexamples a negative temperature gradient is achieved in the same way.

EXAMPLE 2 A tightly wound spiral 18 of iron thread, in which adjacentturns, for example 19 and 20 (FIG. 2a) are in contact with each other,is arranged in accordance with FIG. 2 between two pre-compressedcylinders 21 and 22 of graphite. The iron thread is flat along thecontact surface between adjacent turns and has rounded edges 23 formingthe narrowing or projecting parts. The reaction mixture is heated by anelectric current as previously indicated to a temperature of about l,5lC. and subjected to a pressure of about 75,000 atm. for 4 minutes.

EXAMPLE 3 In accordance with FIG. 3 the solvent body consists of a layerof tightly packed balls 24 of iron. Adjacent balls are thus in contactwith each other. The balls may have a diameter of about 0.5 mm. Oneither side of the layer of iron balls are arranged two pre-compressedgraphite cylinders 25 and 26. Due to their geometrical form, the ballsare provided with narrowing parts in a radial direction, perpendicularto a plane chosen arbitrarily through the center of the ball. Thereaction mixture is heated by an electric current as mentionedpreviously to a temperature of about 1,450" C. and-subjected to apressure of about 60,000 atm. for 9 minutes, whereby large diamonds withwell defined crystals are formed.

EXAMPLE 4 Two loosely wound flat spirals 28 and 29 having gaps 28a and29a, respectively, (FIG. 4a) between adjacent turns 28b,

28c and 29b, 290, respectively, are arranged in accordance with FIG. 4in graphite pre-compressed at approximately 3,000 kp./cm In this casethe solvent bodies consist of the two spirals 28 and 29 which arearranged perpendicular to the pressure direction and current direction.Each solvent body, for example 28, has parts consisting of its turns,two of which have been designated 28b and 28c, and between which partsthere is thus a gap filled by graphite.

The spirals may be of nickel thread or cobalt thread with a diameter ofabout 1 mm. and the gaps'28a and 29a, respectively may be about 1 mm.wide. In the flat spiral according to FIG. 4 the metalthread, from anarbitrary axial plane in the thread, due to its own geometrical form, isprovided with narrowing parts in a radial direction perpendicular tosaid plane. That part of the graphite surrounding the solvent bodies assuch is designated 30 and that part of the graphite arranged in the gapsbetween the turns is designated 30a. The reaction mixture is heated inthe manner previously indicated by an electric current to a temperatureof about 1,550 C. and subjected to a pressure of about 65,000 atm. for 34 minutes, whereby large, well crystallized diamonds are formed.

EXAMPLE 5 In accordance with FIG. 5 the solvent body consists of severalconcentric rings 32, 33, 34 and 35 arranged with gaps 36. The solventbody thus has parts consisting of said rings 32, 33, 34 and 35. Therings may be, for example of a chromiumnickel alloy containing 20percent by weight chromium and percent by weight nickel. Each ring has asquare cross section with a side length of 1.5 mm. for the square. Thedistance between adjacent parts of two rings may be 2 mm. Due to itsgeometrical form each ring is provided with narrowing parts ending inaxially directed edges 37 and 38 and in radially directed edges 39 and40. The edges face the carbonaceous material the part of whichsurrounding the solvent body is designated 41 and that arranged in thegaps between the rings is designated 42. The reaction mixture is heatedin the manner previously indicated by an electric current to atemperature of about l,480 C. and subjected to a pressure of about65,000 atm. for 2 minutes. If rings having quadratic cross section areused, these may for example also be shaped so that they have inner andouter envelope surfaces parallel to the symmetry axis of the ring andend surfaces perpendicular to the symmetry axis. Of course rings having,for example, circular cross section may be used instead of rings havingquadratic crosssection.

Instead of loosely wound spiral or concentric rings in accordance withFIGS. 4 and 5, the solvent body may among other things consist of alayer of balls in which adjacent balls are separated from each other bygraphite.

I claim:

1. Method of manufacturing synthetic diamonds by subjecting a reactionmixture comprising a non-diamond carbonaceous material and a metallicsolvent for carbon having the capacity to convert the carbonaceousmaterial to diamond, in a reaction vessel, to temperatures and pressuresin the diamond stable region, in which the reaction mixture is heated byan electric current led through the reaction mixture to a temperaturesufficiently high to melt the solvent is shaped to extend over thegreater part of the cross section of the reaction vessel transverse tothe direction of the current and arranged substantiallyperpendicular tothe current direction and embedded on all sides in the carbonaceousmaterial, in which the solvent is constituted by a plurality of spacedapart substantially coplanar sections the spaces between which extend inthe direction of the current completely through the solvent body and arefilled by the carbonaceous material, said sections having portionstapering in the direction of the current embedded in the carbonaceousmaterial and the sections being connected together in a unit, so that anegative temperature gradient is effected in the direction from thecarbonaceous material to the solvent body.

2. Method of manufacturing synthetic diamonds by subjecting a reactionmixture comprising a non-diamond carbonaceous material and a metallicsolvent for carbon having the capacity to convert the carbonaceousmaterial to diamond, in a reaction vessel, to temperatures and pressuresin the diamond stable region, in which the reaction mixture is heated byan electric current led through the reaction mixture to a temperaturesufficiently high to melt the solvent, and the solvent is shaped toextend over the greater part of the cross section of the reaction vesseltransverse to the direction of the current and arranged substantiallyperpendicular to the current direction and embedded on all sides in thecarbonaceous material, in which the solvent is constituted by a spirallywound solid member, the coils of which are substantially coplanar andhave portions tapering in the direction of the current embedded in thecarbonaceous material, so that a negative temperature gradient iseffected in the direction from the carbonaceous material to the solventbody.

3. Method of manufacturing synthetic diamonds by subjecting a reactionmixture comprising a non-diamond carbonaceous material and a metallicsolvent for carbon having the capacity to convert the carbonaceousmaterial to diamond, in a reaction vessel, to temperatures and pressuresin the diamond stable region, in which the reaction mixture is heated byan electric current led through the reaction mixture to a temperaturesufficiently high to melt the solvent, and the solvent is shaped as aspirally wound solid member, the coils of which are substantiallycoplanar and spaced apart, and extending over the greater part of thecross section of the reaction vessel transverse to the direction of thecurrent and arranged substantially perpendicular to the currentdirection and embedded on all sides in the carbonaceous material, thespaces between the coils being filled by the carbonaceous material, thecoils beingshaped so as to have portions tapering in the direction ofthe current embedded in the carbonaceous material, so that a negativetemperature gradient is effected in the direction from the carbonaceousmaterial to the solvent body.

2. Method of manufacturing synthetic diamonds by subjecting a reactionmixture comPrising a non-diamond carbonaceous material and a metallicsolvent for carbon having the capacity to convert the carbonaceousmaterial to diamond, in a reaction vessel, to temperatures and pressuresin the diamond stable region, in which the reaction mixture is heated byan electric current led through the reaction mixture to a temperaturesufficiently high to melt the solvent, and the solvent is shaped toextend over the greater part of the cross-section of the reaction vesseltransverse to the direction of the current and arranged substantiallyperpendicular to the current direction and embedded on all sides in thecarbonaceous material, in which the solvent is constituted by a spirallywound solid member, the coils of which are substantially coplanar andhave portions tapering in the direction of the current embedded in thecarbonaceous material, so that a negative temperature gradient iseffected in the direction from the carbonaceous material to the solventbody.
 3. Method of manufacturing synthetic diamonds by subjecting areaction mixture comprising a non-diamond carbonaceous material and ametallic solvent for carbon having the capacity to convert thecarbonaceous material to diamond, in a reaction vessel, to temperaturesand pressures in the diamond stable region, in which the reactionmixture is heated by an electric current led through the reactionmixture to a temperature sufficiently high to melt the solvent, and thesolvent is shaped as a spirally wound solid member, the coils of whichare substantially coplanar and spaced apart, and extending over thegreater part of the cross-section of the reaction vessel transverse tothe direction of the current and arranged substantially perpendicular tothe current direction and embedded on all sides in the carbonaceousmaterial, the spaces between the coils being filled by the carbonaceousmaterial, the coils being shaped so as to have portions tapering in thedirection of the current embedded in the carbonaceous material, so thata negative temperature gradient is effected in the direction from thecarbonaceous material to the solvent body.